Radiation Measurements 41 (2006) 1080 – 1090 www.elsevier.com/locate/radmeas PHITS—a particle and heavy ion transport code system Koji Niita a , * , Tatsuhiko Sato b , Hiroshi Iwase c , Hiroyuki Nose d , Hiroshi Nakashima b , Lembit Sihver e , f a Research Organization for Information Science & Technology (RIST), 2-4 Shirane, Shirakata, Tokai, Naka, Ibaraki 319-1106, Japan b Japan Atomic Energy Research Institute (JAERI), Japan c GSI, Germany d Ishikawajima-Harima Heavy Industries Co., Ltd. (IHI), Japan e Chalmers University of Technology, Sweden f Roanoke College, USA Received 11 May 2005; received in revised form 7 April 2006; accepted 2 July 2006 Abstract The paper presents a summary of the recent development of the multi-purpose Monte Carlo Particle and Heavy Ion Transport code System, PHITS. In particular, we discuss in detail the development of two new models, JAM and JQMD, for high energy particle interactions, incorporated in PHITS, and show comparisons between model calculations and experiments for the validations of these models. The paper presents three applications of the code including spallation neutron source, heavy ion therapy and space radiation. The results and examples shown indicate PHITS has great ability of carrying out the radiation transport analysis of almost all particles including heavy ions within a wide energy range. © 2006 Elsevier Ltd. All rights reserved. 1. Introduction Particle and heavy ion transport code is an essential imple- ment in design and study of spacecrafts and accelerator facil- ities. We have therefore developed the multi-purpose Monte Carlo Particle and Heavy Ion Transport code System, PHITS (Iwase et al., 2002), based on the NMTC/JAM (Niita et al., 2001). The physical processes which we should deal with in a multi- purpose simulation code can be divided into two categories, transport process and collision process. In the transport pro- cess, PHITS can simulate a motion under external fields such as magnetic and gravity. Without the external fields, neutral particles move along a straight trajectory with constant energy up to the next collision point. However, charge particles and heavy ions interact many times with electrons in the material losing energy and changing direction. PHITS treats ionization processes not as collision but as a transport process under an ex- ternal field. The average dE/dx is given by the charge density * Corresponding author. Tel.: +81 29 282 5017; fax: +81 29 287 0315. E-mail address: niita@tokai.rist.or.jp (K. Niita). 1350-4487/$ - see front matter © 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2006.07.013 of the material and the momentum of the particle taking into account the fluctuations of the energy loss and the angular deviation. The second category of the physical processes is the collision with the nucleus in the material. In addition to the collision, we consider the decay of the particle as a process in this category. The total reaction cross section, or the life time of the particle is an essential quantity in the determination of the mean free path of the transport particle. According to the mean free path, PHITS chooses the next collision point using the Monte Carlo method. To generate the secondary particles of the collision, we need the information of the final states of the collision. For neutron induced reactions in low energy region, PHITS em- ploys the cross sections from Evaluated Nuclear Data libraries such as ENDF-B/VI (McLane et al., 1996) and JENDL-3.3 library (Shibata et al., 2002) up to 20 MeV and LA150 up to 150 MeV (Chadwick et al., 1999). PHITS also uses Evaluated Nuclear Data for photon and electron transport below 1 GeV in the same manner as in the MCNP4C code (Briesmeister et al., 1997) based on ITS version 3.0 code (Halbleib et al., 1992). For high energy neutrons and other particles, we have incor- porated two new models, JAM (Nara et al., 2000) and JQMD